Japanese Patent Application Publication No. 2005-32668 (JP-A-2005-32668) discloses a fuel cell catalyst layer made up of a platinum catalyst, an electron conductor made of a carbon black, and a proton-conductive polymer. According to this fuel cell catalyst layer, the proton-conductive polymer is disposed within agglomerates formed by the carbon black and between the agglomerates.
Furthermore, Japanese Patent Application Publication No, 2002-25560 (JP-A-2002-25560) and Japanese Patent Application Publication No. 2002-63912 (JP-A-2002-63912) disclose a catalyst layer that has a carbon particle on which a catalyst metal is supported, and a polymer having proton conductivity. According to this catalyst layer, the polymer has entered pores of agglomerate structures of carbon particles.
Still further, Japanese Patent Application Publication No. 2004-281305 (JP-A-2004-281305) discloses an electrode equipped with a catalyst layer that has a carbon particle having electroconductivity on which a catalyst metal is supported, and a proton-conductive polymer. According to this electrode, the specific surface area of the carbon particle is 200 to 1300 m2/g, and the proton-conductive polymer includes a first proton-conductive polymer whose unit segment size is 5 to 100 nanometers, and a second proton-conductive polymer whose unit segment size is 100 to 1000 nanometers. The large-size second proton-conductive polymer, due to its great molecular chain length and high crystallinity, has a characteristic of being less prone to be swollen by a liquid material, and therefore is expected to restrain the elution of the small-size first proton-conductive polymer.